The present invention relates generally to a near-field optical technology, and more particularly to a knock mode scanning near-field optical microscope controlled by a highly-sensitive near-field distance.
As shown in FIG. 1, a shear force mode scanning near-field optical microscope of the prior art comprises a light source member 1, an optical fiber probe 2, an oscillation member 3, and a signal feedback member 4. The light source member I serves as a light source of the optical fiber probe 2. The optical fiber probe 2 is driven by the oscillation member 3 such that the amplitude and the phase are changed due to the interaction force between the tip of the probe 2 and the surface of a sample 7, and Van der Waals, at the time of resonance frequency and at the time when the probe 2 comes in contact with the surface of the sample 7. The feedback control is brought about by the signal feedback member 4 so as to regulate the height (nm) of the probe 2 on the surface of the sample 7, thereby resulting in the formation of a near-field optical image of the sample 7.
The oscillation member 3 is formed of a forked pillar 5 and a piezoelectric ceramics 16. The forked pillar 5 is attached to the optical fiber probe 2 in the direction of the longitudinal axis of the forked pillar 5. In other words, the forked pillar 5 has a short axis face 8 by means of which the surface of the sample 7, the action force of the tip of the probe 2 and Van der Walls are sensed. As a result, the short axis face 8 is burdened with a shear force mode load. In light of the small area of the short axis face 8 of the forked pillar 5, the short axis face 8 is burdened with a relatively small external force. (Assuming that the load remains unchanged, the external force is in a direct proportion to the area.). In the resonance operation, the amplitude is relatively small. The amplitude is directly proportional to an external force energy stored in the probe 2. As a result, it has a relatively low sensitivity. In the meantime, the rigidity of the entire structure is greater in light of the optical fiber probe 2 and the entire forked pillar 5 being attached along the direction of the longitudinal axis of the forked pillar 5. However, the structure has become less sensitive to the oscillation brought about by an external force.
As shown in FIG. 2, the shear force mode near-field optical microscope of the prior art is exposed to air at the time when the microscopic operation of the sample 7 by the microscope is under way. Under the condition of resonance frequency and in the figure showing the relationship between the peak of amplitude and the sample height, it is observed that the amplitude is smallest at the time when the probe 2 comes in contact with the sample 7. The amplitude change zone is defined as an interaction zone with the change value ranging between 10% and 90%. The interaction zone is divided into a first section with 66 nm conversion interaction zone and with a considerably low sensitivity (inclination), and a second section with 9 nm conversion interaction zone and with a sensitivity of about 0.02 V/nm, which is considerably low. This implies that the shear force mode scanning near-field optical microscope of the prior art has a poor sensitivity and is thus incapable of a precision feedback control.
The primary objective of t he present invention is therefore to provide a knock mode scannin near-field optical microscope having an excellent sensitivity and capable of a precision feedback control.
In keeping with the principle of the present invention, the foregoing objective of the present invention is attained by a knock mode scanning near-field optical microscope, which comprises a light source member, an optical fiber probe, an oscillation member, and a signal feedback member. The optical fiber probe is connected at one end thereof with the light source member such that other end of the optical fiber probe forms a near-field point source of light. The oscillation member is formed of a piezoelectric ceramics and a suspension arm which is attached at one end thereof with the optical fiber probe. The piezoelectric ceramics is mounted on the suspension arm. The signal feedback member uses a harmonic wave signal to drive the piezoelectric ceramics so as to bring about a change in the amplitude and the phase of the optical fiber probe, thereby resulting in a feedback control.
The foregoing objective, features, functions, and advantages of the present invention will be more readily understood upon a thoughtful deliberation of the following detailed description of a preferred embodiment of the present invention with reference to the accompanying drawings.